The use of membranes, coatings and capsules for the controlled release of liquid materials is well known in the art of both agricultural and non-agricultural chemicals. In agriculture, controlled release techniques have improved the efficiency of herbicides, insecticides, fungicides, bactericides, and fertilizers. Non-agricultural uses include encapsulated dyes, inks, pharmaceuticals, flavoring agents, and fragrances.
The most common forms of controlled-release materials are coated droplets or microcapsules, coated solids including both porous and non-porous particles, and coated aggregates of solid particles. In some instances, the coating is porous and the entrapped material is released to the surrounding medium at a slow rate by diffusion through the pores. In other instances, the encapsulating film is water-soluble and the encapsulated material is released when the capsule is placed in contact with water. Still other coatings release the entrapped material when the coating is ruptured by external force.
This invention relates to porous coatings. In addition to providing controlled release, these coatings facilitate the dispersion of water-immiscible liquids into water and water-containing media, such as wet soil. Droplets encapsulated in this manner are particularly useful in agriculture, where water from irrigation, rain, and water sprays is frequently present. A variety of processes for producing such capsules is known.
Interfacial polymerization is one type of process for producing these capsules. Typically, interfacial polymerization involves preparation of two distinct phases. One of the film-forming reactants is dissolved in an aqueous phase and the other reactant is dissolved in a hydrophobic phase. Reaction between the two film-forming reactants occurs at the phase interface when the phases are placed in contact with each other.
A second type of interfacial polymerization process is disclosed in U.S. Pat. Nos. 4,046,741 (Scher, Sept. 6, 1977) and in copending application Ser. No. 922,473, now U.S. Pat. No. 4,285,720. Applicant's process differs from typical interfacial polymerization processes in that one of the film-forming reactants is formed in situ. Material to be encapsulated and at least one polyisocyanate are present in an organic phase. A surfactant and a protective colloid are present in an aqueous phase. After dispersion of the organic phase into the aqueous phase and heating, the isocyanate monomers react with water at the phase interface to form an amine. This amine then reacts with remaining isocyanate monomers to form a polyureamicrocapsule wall which encapsulates the "material to be encapsulated." The product of this process is a formulation and includes the microcapsules dispersed in water.
The purpose of the protective colloid which is present in the aqueous phase of Applicant's process is to prevent recombination of particles during the wall formation step. Among the protective colloids previously disclosed are polyacrylates, methylcellulose, polyvinyl alcohol, polyacrylamide and poly(methylvinyl ether/maleic anhyride).
Pesticide loading refers to the amount of pesticide present in a given quantity of formulation. The maximum pesticide loading which can be achieved using any one of the previously disclosed protective colloids is about 2.5 pounds (1b) of pesticide/gallon (gal) of formulation. Above that level, recombination, foaming or gellation may become a problem.